1. Field of the Invention
This invention is concerned with protective coatings for wear-resistant elements intended for severe operating conditions and with methods of depositing such coatings on the wear-resistant substrates or inserts.
2. Prior Art
Cemented carbides, also known as sintered carbides, are solid and coherent masses made by pressing and sintering a mixture of powders of one or more metallic carbides and a much smaller amount of an iron group metal, such as cobalt, to serve as a binder metal. These carbides may be used as tools or inserts for machining, milling, blanking, and drawings operations; also as shaping dies, spinning dies, and for many other applications. Such tools are capable of performance beyond the limits of high speed steels and in many cases are suitable for use on very hard abrasive materials and on tough alloys. Cemented carbides are widely used for structural parts and tools subject to intense wear or other service loads that require high compressive strength. Suitable carbides for such purposes include the carbides of tungsten, titanium, tantalum, columbium, molybdenum, vanadium, chromium, zirconium, and hafnium.
Cemented carbides because of their unique strength and hardness are frequently subjected to conditions of intense wear. The manner and rate of wear depends very largely on the use and service conditions of the cemented carbide part. Wear is frequently caused by mechanical abrasion which can be greatly intensified by diffusion processes when operating at elevated temperatures. Corrosion is also a cause in the wear of such parts, for example, when cemented carbide is used in corrosive media or when oxidation in the air takes place at elevated temperatures. When cemented carbides are used for shaping of other parts, either by machining and nonchipping shaping operations or by other processes, the cemented carbide parts are not only subjected to heavy mechanical stresses but there is frequently also intense heating which greatly accelerates the wear.
In the machining of long-chipping and short-chipping materials, as for example, steel or cast iron, respectively, wear on the cutting edge can occur as a result of cratering of the rake face and abrasion of the clearance face. Furthermore, the chips can adhere or weld onto the cutting edge of the part and cause chipping or splintering of the edge. In interrupted cuts, crack formation may be caused by rapid temperature changes and splintering can occur from heavy impacts.
It has now been discovered that wear-resistant stratified coatings composed of a number of layers of certain different compositions provide a number of significantly improved results of an unpredictable nature as described hereinafter, particularly when these coatings are employed as protective wear-resistant coatings on cemented carbide substrates and other hard material bases. The coated articles have many uses for metal working and other purposes that involve exposure to mechanical wear and abrasion.